As one of systems of this type, Japanese Utility Model Laying-Open Publication No. 55-35570 entitled "Music Box Having A Rythm-responsive Flickering Lamp" is configured to generate an electricity simultaneously with playing music. Since the music box has a coil secured to a rotary shaft of its rotaty member, it has an acceptable electricity-generating function. However, in order to connect the rotary coil to a circuit, it requires a brush or other arrangement. This produces a noise which is an obstruction to the music played by the music box. Further, the music box is configured to play the music at an optimum speed when a lamp circuit or other load is conected to the coil. Therefore, when no load is connected, the music box is very small in speed control effect because the spiral spring is released merely under a control of the inertia of the rotary shaft with or without an addition of magnetic attraction power. As a result, the music is played at a very high speed, and the stored energy of the spiral spring is exhausted in a short time. This causes that the play does not provide an expected melody and that a pin of a drum hits a vibration flap violently and damages the flap. Beside this, a music box in general is manufactured by first completing the major body thereof and subsequently incorporating various attachments therein. During the manufacturing process of the major body, a test play is required by winding the spiral spring. However, since the above-described prior art music box has a very poor speed control function unless the magnet and the lamp circuit are connected, such a test play is almost impossible.